Apparatus for machining metals electrochemically

ABSTRACT

AN APPARATUS FOR THE ELECTROCHEMICAL MACHINING OF FLAT METAL SURFACES WHICH UTILIZES A POOL OF VISCOUS ELECTROLYTE OF SUFFICIENT VISCOSITY TO SUPPORT A WORKPIECE AND SPACE THE WORKPIECE VERY SLIGHTLY FROM THE SURFACE PLATE, AS WELL AS TO FACILITATE MOVEMENT OF THE WORKPIECE OVER THE SURFACE PLATE. MOVEMENT OF THE WORKPIECE IN COMBINATION WITH VARIOUS VISCOSITES OF THE VISCOUS ELECTROLYTE ARE UTILIIZED TO OBTAIN THE DEGREE OF FLATNESS DESIRED.

May 25, 1971 R. K. SEDGWICK' APPARATUS FOR MACHINING METALS ELECTROCHEMICALLY Filed Dec. 4. 1967 2 Sheets-Sheet 1 INVENTOR. ROBERT KSEDG'W/CK May 25, 1971 R. K. SEDGWICK 2 Sheets-Sheet 2 Filed Dec O I m w m v III R c 6 .1 3 b t T 2 a llllll II III I l I INVENTOR. ROBERT K. SLDGW/Ck BY hm flfljz.

United States Patent O1.

3,580,834 APPARATUS FOR MAC ill l- G METALS ELE'CTROCHEMI ALLY Robert K. Sedgwick, Waukesha, Wis., assignor to Kearney & Trecker orporation, West Allis, Wis. Filed Dec. 4, 1967, Ser. No. 687,776 Int. (31. B23p 1/02 US. Cl. 204-224 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to electrochemical machining and more particularly to the electrochemical machining of flat surfaces.

In the making of gibs and ways for machine tools, the customary method of finishing the fiat surfaces of the gibs and ways is by the use of grinding procedures. In grinding, there is a tendency for slight warping, requiring the manual scraping of the surface to restore flatness. Manual scraping is a time-consuming operation and requires the services of a skilled craftsman. A method is needed that will reduce the time required for finishing a gib or way and thereby lower the costs involved.

In electrochemical machining, the workpiece is the anode and made positive; the machining tool is the cathode and is made negative. The gap or space between the anode and cathode is filled with an electrolytic solution normally under pressure and operative to carry an electric current from the positive workpiece to the negative machining tool. Due to the electric current, the metal of the workpiece surface will undergo a chemical dissolution wherein a given amount of metal is removed from the workpiece surface.

In previous electrochemical machining apparatus, pumping means were used to circulate large quantities of electrolyte between the surfaces of the workpiece anode and the cathode forming tool, which were urged toward one another under controlled pressure.

SUMMARY OF THE INVENTION According to this invention, there is provided a new, simplified apparatus and method for machining flat bearing surfaces or enlarged flat metal surfaces, such as machine ways and gibs. A pool of viscous electrolyte is poured on a horizontal flat cathode plate constituting a forming tool. A workpiece is placed on the pool of electrolyte which is of sufficient viscosity to support a moving workpiece and to keep the workpiece separated from the cathode plate by an extremely small distance. The workpiece is then connected to an electrical potential of positive polarity and the cathode surface plate is connected to the negative side of the electrical potential source. The workpiece is then moved by hand or by a machine that will produce a random path of travel over the pool of electrolyte. The random path of travel over the electrolyte will serve to continually position the workpiece over fresh areas of the electrolyte. This will effect the continuous mixing of the electrolyte with the products resulting from the electrochemical dissolution of the flat bearing surface of the workpiece. Very little voltage is required so electric shock is no hazard and all parts of the 3,589,834 Patented May 25, 1971 apparatus may be freely handled. If desired, the viscosity of the electrolyte can be changed periodically to reach any degree of flatness desired. By using a less viscous electrolyte as the flatness of the workpiece improves, the distance between the workpiece and the cathode surface plate becomes smaller allowing for a finer machining effect.

It is the general object of this invention to provide a method and apparatus for finishing fiat surfaces of workpieces that will completely eliminate the requirement for grinding and manual scraping of the flat metal surfaces.

Another object of this invention is to provide a method for electrochemical machining of flat metal surfaces that materially reduces the amount of electrolyte used in the process thereby effecting a substantial reduction in the manufacturing cost.

Still another object of the present invention is to pro vide a method and apparatus for electrochemical machining of fiat metal surfaces that eliminates the necessity of continuously circulating the electrolyte thereby eliminating pumping equipment in the apparatus.

It is a further object of this invention to provide a means whereby gibs, ways and other flat surfaces can be finish machined economically and rapidly under commercial production conditions.

The foregoing and other objects of this invention, which will become more fully apparent from the following detailed description, may be achieved by the exemplifying apparatus depicted and set forth in the specification in connection with the accompanying drawings in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of an electrolytic machining apparatus incorporating the features of the present invention with parts broken away to show the brush holder, slip ring, and drive assemblies;

FIG. 2 is an enlarged fragmentary view in elevation of the vertical column, shown in FIG. 1, With parts broken away to show the brush holder and slip ring assemblies;

FIG. 3 is a view in cross section of the shaft taken along a plane represented by the line 3-3, in FIG. 2; and

FIG. 4 is a plan view of the apparatus showing the drive mechanism for effecting the paths of random motion that the workpiece travels on the cathode surface plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and more specifically to FIG. 1 thereof, an electrochemical machining apparatus incorporating the features of the present invention comprises generally a frame 10 which fixedly supports a flat cathode plate 11. The cathode plate 11 acts as the forming tool in the electrochemical machining process and is secured to the top of the frame 10 by a plurality of insulated bolts 13. A pool of viscous electrolytic fluid 14, which is of suflicient viscosity to support a moving workpiece W.P., is poured on the surface of cathode plate 11. The viscous electrolyte 14 separates the moving workpiece very slightly from the cathode plate 11 as well as facilitating movement of the workpiece thereover.

For electrochemical machining of a workpiece, the workpiece W.P. is positive to consititute an anode and the tool as represented by the cathode plate 11 is negative. As shown in FIG. 1, a direct current source of electricity such as a storage battery 15 has its negative terminal 17 connected by a cable 18 to the cathode plate 11 by a cable lug 19 and bolt 20. The positive side 22 of the power supply 15 is connected by a cable 23 to an on-oif switch 24 and then is continued on to a rheostat 26, which is used to control the current flow to the workpiece W.P. that is being machined. The on-oif switch 24 and rheostat 26 are mounted on a front panel 27 of the frame 10. From the rheostat 26 the positive side of the power supply is carried by a cable 29 to a brush holder assembly, which is generally indicated by reference number 30. The cable 29 and the brush assembly 30 are located within a random motion mechanism 70, to be subsequently described, which imparts oscillatable and rotatable motion to the workpiece.

As shown in FIG. 2, the brush holder assembly 30 has an insulating bottom plate 31 which is secured to the internal bottom surface of a horizontally extending support arm 32 of the random motion mechanism 70. A brush 35 is pressed by a spring 36 against a current conducting slip ring 38 which is mounted on a split insulating ring 39 which, in turn, is secured to a hollow vertical shaft 40. Vertical shaft 40 is provided with an opening 41, as shown in FIG. 3, to allow a lead wire 43 from the slip ring 38 to be connected to an insulated cable 45 which runs down within the hollow center of shaft 40. Cable 45 extends downwardly and out of the lower end of the shaft 40 and thence through an arm 46, and is attached to a vertical metal rod 48. Rod 48 is freely supported within an insulating bushing 50 which is secured in a vertical bore 51 formed in the arm 46. The workpieces are provided With a circular recess 52 engaged by the lower end 53 of the rod 48. The weight of the metal rod 48 will supply sufficient electrical contact between the bottom 53 of the rod and the workpiece. Combined oscillatable and rotatable movement of the arm 46 in a horizontal plane effects like movement of the rod 48, which is connected to move the workpiece W.P. in a random horizontal path along the cathode plate 11.

As electric current is passed from the positive workpiece to the negative cathode plate 11 through the electrolytic solution, a material removal action occurs at the workpiece surface.

As shown in FIG. 1, a vertical bracket 56 mounted on the left side of housing 10 supports a tank 57 for electrolytic fluid that is transmitted via a discharge tube 59 to a discharge valve 60. Valve 60 is operable in known manner to control the output flow of electrolyte from the tube 59 which is movable above the cathode plate 11 for directing an additional supply of electrolyte to the middle of the cathode plate 11. As this occurs, the original electrolytic fluid will overflow the edges of the cathode plate 11 and run into a sump 63 located beneath the cathode plate 11. The spent electrolyte will runout an outlet drain 64 located in an external Wall of the frame 10. Instead of running the electrolyte out of a drain, the spent electrolyte could be stored in a tank to be reclaimed at a later date.

Also shown in FIG. 1, to the right and top of the frame 10 is a random motion mechanism indicated by general reference number 70 which supplies the drive for effecting oscillatable and rotatable movement of arm 46. The random motion mechanism 70 is attached to the frame 10 and is used to move thewor-kpiece in a random path over the whole surface of the pool of electrolyte to con tinually position the workpiece over fresh areas of the electrolyte 14. The random motion apparatus 70 can be replaced by an operator who can manually move the workpiece around on the viscous electrolyte solution. The surface of the workpiece could be tilted by the operator applying local pressure on the workpiece which will cause the effect to be concentrated and enables the operator to increase or decrease the taper of the flat surface of the workpiece. Varying amounts of electrochemical material removal action will occur at the workpiece surface depending on the distance between the workpiece and the cathode plate 11. The distance between the workpiece and the cathode plate 11 is affected by the viscosity of the electrolyte which can be changed by adding more or less thickening agent to the electrolyte tank 57. Combinations of movement of the workpiece and different degrees of viscous electrolyte are utilized to obtain the degree of flatness desired. Since the operator is working an electrochemical process that operates with an electrical potential of one to ten volts, there is no hazard from electrical shock. A current density of 3 amperes/sq. inch has been found to work satisfactorily and with the present apparatus a number of workpieces can be electrochemically machined using the same electrolytic fluid.

Irrespective of which electrolytic solution is provided for use in the machine, it has the characteristics hereinbefore described. First, it has sufiicient viscosity to support a flat workpiece an extremely slightly spaced distance above the surface of the fiat surface presented by the cathode plate 11. Second, in suporting the flat workpiece slightly, the viscosity of the solution is sufficient to facilitate movement of the workpiece along its random paths of movement. Third, during the random paths of movement of the workpiece, the electrolytic solution coacts with the low amperage current to facilitate a material removal action at the workpiece surface until the requisite degree of flatness is achieved. Fourth, the workpiece material removed by the electrochemical action flows with the spent electrolyte to the sump, and is continually replenished by electrolytic fluid from the metering means.

As viewed in FIG. 1, the random motion mechanism includes the arm 46 which supports the axially movable rod 48. Arm 46 is keyed to a vertical shaft 40 which is rotatably supported by bearings 71 and 72 carried toward the outer end of the support arm 32 which is secured at its opposite end to a rotatable support column 80. Shaft 40 is keyed to a driven pulley 74 which is rotated by a belt 75 connected to a drive pulley 76 rotatably supported at the upper end of the column which is supported for limited angular rotation relative to the support frame 10, as will hereinafter be explained.

Pulley 76 is keyed to vertical shaft 78 which is rotatably supported by an upper bearing 77 and a lower bearing 79 carried by the independently pivotable column 80'. Shaft 78 has keyed to its lower end a gear 82 driven by a worm gear 83 havingits shaft secured to a pulley 85 which is driven by a motor 87 by means of a slipping belt 86, as shown in FIGS. 1 and 4. The rotary motion transmitted by belt 86, via the vertical shaft 78, belt 75, and depending shaft 40 rotates the horizontal arm 46 throughout a 360 circle, as illustrated in FIG. 4 by dotted line 90, to effect corresponding rotary movement of the drive rod 48 carried thereby.

Column 80 is rotatably supported for limited pivotable movement in bearings 91 and 92 which are carried by a support base 94 attached to the frame 10. Column 80 is pivotably rotatable through an arc of approximately 30, as shown by dotted lines 96 in FIG. 4, simultaneously with the rotatable movement of the arm 46. This approximate 30 movement is obtained from a drive mechanism comprising the motor 87, belt 98, pulley 99, worm gear 100, gear 101, pivoting link 102 and arm 104. These components and their relationships are shown in FIGS. 1 and 4. Motor 87 drives belt 98 which, in turn, rotates pulley 99. Worm gear 100, which is connected to pulley 99, turns as pulley 99 rotates. Rotational drive from the worm gear 100 is transmitted to meshed gear 101, which is 'provided with a hub pivotably pinned to one end of the link 102.

Arm 104 is a lateral extension of hub 105 and is pivotably pinned to the other end of link 102. Hub 105 is secured to vertical column 80 and consequentially column 80 will turn with hub 105. The selection of any one of the plurality of holes in arm 104 depend on the angular displacement desired for column 80. Whatever hole is selected determines the amount of movement arm 104 will make for every revolution gear 101. By selecting a hole which makes arm 104 longer, there is provided a resulting smaller angular displacement of hub 105 and consequently column 80.

Slippage of the belts 86 and 98 assures constantly changing angular relationships between arm 46 and column 80, producing the necessary degree of random movement of the workpiece path. I

To summarize, the present invention includes a method and apparatus for electrochemically machining flat surfaces on metal workpieces. A pool of viscous electrolyte is used to space the moving workpiece very slightly from the cathode surface plate, as well as to facilitate movement of the workpiece therealong. An operator or a random motion mechanism is used to move the workpiece over the pool of electrolyte. The workpiece is connected to the positive side of a direct current power supply. The cathode surface plate is connected to the negative side of the direct current power source. A current density of approximately 3 amperes/sq. inch is used with a very small spacing between the workpiece and cathode surface plate. A very low voltage is maintained. The present invention provides a means whereby gibs, ways and other flat surfaces can be machined economically, rapidly and safely under commercial production conditions.

From the above description of a preferred embodiment of my invention it will be apparent that variations in any of the structures may be made without departing from the spirit and scope of the invention and that the scope of the invention is to be determined from the scope of the following claims:

The principles of this invention having now been fully explained in connection with the foregoing description, I hereby claim as my invention:

1. Apparatus for electrolytically removing material from an electrically conductive workpiece to provide thereon a flat bearing surface comprising:

a frame;

a horizontal flat cathode plate constituting a flat work forming tool supported by said frame, said horizontal work forming tool being operatively disposed to maintain on its surface a uniform film of selectively viscous electrolytic fluid comprising a uniform current transmitting film adapted to resiliently support a workpiece for movement;

a reservoir connected to supply a predetermined variable volume of electrolytic fluid to the surface of said work forming tool;

a fluid conductor tube including valving means selectively adjustable and operatively connected to transmit fluid from said reservoir and maintain a predeterminately thick film of viscous electrolytic fluid on the surface of said work forming tool;

a sump positioned to in turn receive excess fluid from the surface of said work forming tool to insure a continuous circulation of a uniformly thick film of fluid over said surface;

an electric power source including conductor means removably connecting the positive side of said power source to a workpiece and separate conductor means connecting the negative side of said power source to said work forming tool in a manner that a material removal is effected on the underside of a workpiece by transmission of positive current through a film of selectively viscous fluid to said negative work forming tool;

a power driven arm movably carried by said frame for horizontal movement along an irregular path parallel to said flat forming tool and being releasably connected to effect irregular horizontal movement of a workpiece along a film of current passing fluid presented by said work forming tool; and,

power drive means connected to effect horizontal bodily movement of said arm along a selectively varied irregular path for effecting corresponding irregular movement of a workpiece in fluid supporting relationship along said forming tool.

2. Apparatus according to claim 1 wherein said means to effect irregular horizontal bodily movement of a workpiece includes a driver opening presented on the upper face of a workpiece to be machined, and comprising:

a workpiece engaging driver rod carried by said power driven arm for vertical movement into gravity urged engagement with a driver opening presented by a workpiece to be machined, said driver rod being operative to transmit both electrical energy and motive power from said irregularly driven arm to move a workpiece in an irregular path of travel along a selectively viscous film of fluid electrolyte circulated over the surface of' said work forming tool.

3. Apparatus for electrically removing material from the underside of an electrically conductive workpiece to provide a flat bearing surface and comprising:

a horizontal cathode plate comprising a work forming tool adapted to present on its upper surface a uniformly thick film of selectively recirculating current transmitting electrolytic fluid, said horizontal work forming tool and the film of fluid presented thereby cooperating to provide a selectively resilient bearing support for maintaining a workpiece in fluid supported current transmitting engagement with said work forming tool;

a supply tank including a discharge tube adjustable connected to supply electrolytic fluid of selectively predetermined viscosity and being operatively connected to supply a predeterminately thick film of electrolytic fluid to the surface of said work forming tool;

a sump adapted to receive excess fluid from said work support and cooperating therewith to provide thereon a continuously recirculating film of fluid of selected viscosity and predetermined thickness;

a source of electric energy including a first conductor releasably connected to transmit positive current to a workpiece movably supported for horizontal movement in fluid supported relationship by said tool support, said source of energy connected via a second conductor to transmit negative current to said tool support for transmission via the selectively viscous film of recirculating fluid presented thereby to a workpiece;

a power driven arm means including a work engaging metal driver rod carried in position to releasably engage an electrically conductive workpiece and being selectively operative to move the engaged workpiece along an irregular path in a continuously variable fluid support path on said work forming tool;

said first conductor including a brush assembly and a slip ring assembly connected to be frictionally engaged by said brush assembly during movement of said arm; and,

power drive means for moving said power driven arm means along said irregular path.

References Cited UNITED STATES PATENTS 2,868,705 1/1959 Baier ct a1. 204-1405 2,965,556 12/1960 Damgaard 204140.5 3,293,162 12/ 1966 Sullivan 204-140.5 3,337,434 8/1967 Jamieson et a1. 204143 HOWARD S. WILLIAMS, 'Primary Examiner S. S. KANTER, Assistant Examiner 

